1. Field of the Invention
The present invention relates generally to a voltage regulator. More particularly, the present invention relates to a voltage regulator apparatus capable of improving the transient response of the voltage regulator.
2. Description of the Related Art
To supply a constant voltage from a voltage source to a load, a voltage regulator is generally installed between the voltage source and the load.
FIG. 1 shows a conventional voltage regulator including an error amplifier 101 and an NMOS transistor 103. FIG. 2 shows another conventional voltage regulator including an amplifier 105 and a PMOS transistor 107. Both types of the foregoing conventional voltage regulators suffer from stability problems related to transient response of output voltage. As a way to improve the transient response, a capacitor is usually installed at the output terminal. However, under certain circumstances, for example, when a voltage regulator is used for multi-media card (MMC) applications, it is not desirable to use such an external capacitor for improving the transient response. Where an MMC is operated at dual voltage (e.g., 3.3 V and 1.8 V), voltage regulators are usually required to provide a stable output voltage without the use of an external capacitor. Thus, there is a problem to provide a stable output voltage while not using an external capacitor.